Method and system for locating a mobile terminal

ABSTRACT

The present invention relates to a method and system for locating a mobile terminal addressed in a location service request by an overlay identity. A database ( 60 ) is accessed to obtain a first routing information of the mobile terminal based on the overlay identity, and the first routing information is then used to access a sub-scriber database ( 40 ) in order to derive a second routing information and a cellular identity of the mobile terminal ( 10 ), based on which a location service of the cellular network is initiated. Thereby, a LCS clients of the overlay system (e.g. IMS) can be supported in current LCS services to enhance their functionality.

FIELD OF THE INVENTION

The present invention relates to a method and system for locating amobile terminal in a cellular network based on a request received froman overlay system, such as a IP (Internet Protocol) Multimedia Subsystem(IMS).

BACKGROUND OF THE INVENTION

In general, overlay systems may be provided in cellular or fixednetworks for enabling network operators to offer specific services basedon and built upon applications, services and protocols not supported intheir networks. The intention is that such services will be developed bythe network operators and other third party suppliers using themechanisms provided by external networks, such as the Internet or otherexternal network systems or subsystems.

Recently, an IP Multimedia core network Subsystem (IMS) has beendeveloped which comprises all core network elements for provision ofmultimedia services. This includes a collection of signalling and bearerrelated network elements as defined e.g. in the Third GenerationPartnership Project (3GPP) specification TS 23.002. IP Multimediaservices are based on an IETF (Internet Engineering Task Force) definedsession control capability which, along with multimedia bearers,utilizes the PS (Packet Switched) domain of the cellular network. Inorder to achieve access independence and to maintain a smooth operationwith wireless terminals across the Internet, the IMS attempts to beconformant to IETF “Internet Standards”. Therefore, the interfacesspecified conform as far as possible to these standards for the casewhere an IETF protocol has been selected, e.g. SIP (Session InitiationProtocol). The IMS enables the convergence of, and access to, voice,video, messaging, data and to web-based technologies for the wirelessuser, and combines the growth of the Internet with the growth In mobilecommunications.

As already mentioned, the IMS utilizes the PS domain to transportmultimedia signalling and bearer traffic. The PS domain maintains theservice while the mobile terminal moves and hides these moves from theIMS. The IMS is independent of the CS (Circuit Switch) domain althoughsome network elements may be common with the CS domain. This means thatit is not necessary to deploy a CS domain in order to support an IMSbased network. A User Equipment (UE) (or mobile station (MS)) consistsof a mobile equipment (ME with a valid USIM (Universal MobileTelecommunications System Subscriber Identity Module) (or SIM(Subscriber Identity Module)) attached. In the following, theabbreviation “UE” refers both to MS and user equipment, even those usedfor emergency calls, which do not have a valid SIM or USIM.

A UE accessing an IMS service requires an IP address which can belogically part of the visited network GPRS IP addressing domain. Thereare various identities which may be associated with a user of IPmultimedia services. Every IMS subscriber has one or more public useridentities. The public user identity is used by any user for requestingcommunications to other users. For example, this might be included on abusiness card. Both telecom numbering and Internet naming schemes can beused to address users depending on the public user identities allocatedto the users. The public user identity may take the form of a SIP URL(Uniform Resource Locator) as defined in RFC 2543 and RFC 2396, or anE.164 number. At least one public user identity may be used to identifythe user's information within a subscriber database, e.g. the HomeSubscriber Server (HSS), e.g. during mobile terminated set-up.

A location service (LCS) feature in UMTS and GSM (Global System forMobile Communications) provides a mechanism to support mobile locationservices for operators, subscribers and third party service providers.Location services may be considered as a network provided enablingtechnology consisting of standardized service capabilities which enablethe provision of location applications. The applications may be serviceprovider specific. In general, LCS is a service concept in a systemstandardization. LCS specifies all necessary network elements andentities, their functionalities, interfaces as well as communicationmessages to implement the positioning functionality in a cellularnetwork. Positioning is a functionality which detects a geographicallocation of e.g. a mobile terminal. Principles and/or algorithms onwhich the estimation of the geographical location is based may be e.g.AOA, TOA or TDOA. For example, the Global Positioning System (GPS) isbased on TOA while OTDOA and E-TD (on GSM) are based on TDOA.

The positioning of the UE is a service provided by the access network.In particular, all access networks (e.g. UMTS Terrestrial Radio AccessNetwork (UTRAN), GSM/EDGE (Enhanced Datarate for GSM Evolution) RadioAccess Network (GERAN), which facilitate determination of the locationsof UEs, shall be able to exchange location information with a corenetwork as defined in the 3GPP specification TS23.271, when connected toa core network.

By making use of the radio signals, the capability to determine the(geographic) location of the UE can be provided. The locationinformation may be requested by and reported to a client (application)associated UE or by a client within or attached to the core network. Thelocation information may also be utilized internally in a system, forexample, for location assisted handover or to support other features,such as home location billing. The position information may be reportedin standard, e.g. geographical coordinates, together with thetime-of-day and the estimated errors (uncertainty) of the location ofthe UE according to the 3GPP specification TS 23.032. There are manydifferent possible uses for the location information. As alreadymentioned, the positioning feature may be used internally by theGSM/UMTS network (or attached networks), by value-added networkservices, by the UE itself or through the network and by the thirdparties' services. The positioning feature may also be used by anemergency service. Although LCS has been defined for the CS and PSdomains of cellular networks, it has not yet been defined for the IMSdomain. Currently, the LCS service does not support IMS LCS clients tobe addressed by IMS identities.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodand system for locating a mobile terminal addressed by an overlayidentity used in an overlay system, e.g. an IMS identity used in theIMS.

This object is achieved by a method of locating a mobile terminal in acellular network, said method comprising the steps of:

receiving a location service request including an overlay identity of anoverlay system;

accessing a database storing a first routing information of said mobileterminal based on said overlay identity;

Using said first routing information to access a subscriber database inorder to derive a second routing information and a cellular identity ofsaid mobile terminal; and

initiating a location service of said cellular network based on saidderived second routing information and cellular identity.

Additionally, the above object is achieved by a system for locating amobile terminal in a cellular network, said system comprising:

a gateway node for receiving a location service request including anoverlay identity of said mobile terminal in an overlay system;

a database storing a first routing information of said mobile terminal;

wherein said gateway node is arranged to access said database based onsaid overlay identity, to use said first routing information for anaccess to a subscriber database in order to derive a second routinginformation and a cellular identity, and to initiate a location serviceof said cellular network based on said derived second routinginformation and cellular identity.

Furthermore, the above object is achieved by a gateway node forinitiating a location service for locating a mobile terminal in acellular network, said gateway node being arranged to read a firstrouting information from a database based on a received overlay identityof said mobile terminal in an overlay system, to use said first routinginformation for an access to a subscriber database in order to derive asecond routing information and a cellular identity, and to perform saidinitiation based on said derived second routing information and cellularidentity.

Accordingly, an address mapping functionality is provided for enabling alocation service for clients in overlay systems to be addressed byoverlay identities, using existing LCS functionalities.

Preferably, other identities of said mobile terminal may be derived fromsaid subscriber data base in said subscriber data base access step. Inparticular, the other identities may be stored in a network elementhaving a mobile location function. Thereby, signaling requirements forderiving the other identities of the mobile terminal in future locationservice requests can be reduced significantly. The overlay identity maybe an IMS identity, in particular a SIP URL.

Furthermore, the first routing information may be a country code, e.g. aMobile Country Code (MCC), and a network code, e.g. Mobile Network Code(MNC), of said mobile terminal.

The subscriber database access step may preferably be performed by usinga MAP query, such as a MAP-SEND-ROUTING-INFO-FOR-LCS service function.

The cellular identity may be an MSISDN or IMSI, and the second routinginformation may be an address of a network element having a switchingfunction in the cellular network.

The gateway node may be a Gateway Mobile Location Center (GMLC). Thedatabase may be comprised in the gateway node or may be a separateexternal entity.

The subscriber database may be a Home Location Register (HLR) of thecellular network. In this case, the HLR may be arranged to derive thesecond routing information and the cellular identity by performing aquery to a Home Subscriber Server. Furthermore, the HLR may be arrangedto derive other identities of the terminal device.

Preferably, the database may be arranged to provide a mapping functionbetween the first routing function and the overlay identity of theterminal device.

Furthermore, the gateway node may be arranged to store the secondrouting information and/or the cellular identity, for further use.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described in greaterdetail based on a preferred embodiment with reference to theaccompanying drawings, in which:

FIG. 1 shows a network architecture for implementing a location servicefunction according to the preferred embodiment of the present invention;

FIG. 2 shows a signaling diagram indicating exchanged signaling messagesand procedures in a location service function according to the preferredembodiment of the present invention; and

FIG. 3 shows a table indicating parameters of a MAP query function usedin the preferred embodiment;

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment will now be described based on an LCSarchitecture in a UMTS network as shown in FIG. 1. According to FIG. 1,a reference point, called Le Interface, is shown between an LCS server(here: GMLC 50) and an LCS client 80 which, in the present embodiment,is an IMS server or application. The Le reference point is described inthe 3GPP Specification TS 22.071. However, there may be more than asingle LCS network interface to several different LCS clients or othernetworks. These networks may both differ in ownership as well as incommunications protocol. The network operator may define and negotiateinterconnection with each external LCS client or other network. Ingeneral, an interface differs from a reference point in that aninterface is defined where specific LCS information is exchanged andneeds to be fully recognized.

Furthermore, an interface called Lg is arranged to connect twoindependent LCS networks, e.g. different PLMNs (Public Land MobileNetworks) for message exchange. The LCS functional entities are groupedinto an LCS client functional group and an LCS server functional group.The LCS server functional group consists of functions in the UMTS PLMNsupporting LCS, e.g. a client handling component, a system handlingcomponent, a subscriber handling component, and a positioning component.The LCS client 80 contains an LCS component with one or more clients,which by using location information can provide location based services.In particular, the LOS client 80 is a logical functional entity thatrequests from the LCS server in the PLMN location information for one ormore than one target UE, i.e. a UE 10 shown in FIG. 1, within aspecified set of parameters such as Quality of Service of QoS.

In the present architecture shown in FIG. 1, the LCS client 80 residesin an external entity belonging to an overlay system, i.e. the IMS. Viaa location service request, the LCS client 80 communicates with the LCSserver, i.e. GMLC 50, to request for the location information of the UE10. Attributes identified by the location service request may be targetUE, LCS identity, state, event, requested QoS information, localcoordinate reference system, and/or geographical area. A locationservice response is sent to the LCS client 80 as the result of thelocation service request issued by the LCS server. Attributes identifiedfor the location service response may be the location indication of theUE 10 in geographical coordinates, the location of the UE 10 as anellipsoid with axes and direction of all axes, an estimated achievedQoS, and/or an indication when UE 10 enters or leaves the geographicalarea.

FIG. 1 illustrates generally the relation of the LCS client 80 andservers in the core network with a GERAN 20 and a UTRAN 30. The LCSentities within the access networks communicate with the core networkconsisting of a 2G-MSC 22 of the CS domain, a 2G-SGSN 24 of the PSdomain, a 3G-SGSN 32 of the PS domain, and an MSC server 34 of the PSdomain across A, Gb and lu interfaces. Communication among the accessnetwork LCS entities makes use of the messaging and signalingcapabilities of the access network.

Furthermore, a subscriber database, i.e. a HLR/HSS 40 is provided forstoring subscriber specific data of the UE 10 and other mobile terminalsor equipments. It is noted that the HLR and HSS may be arranged atdifferent locations, while the HLR part may include both 2G-HLR and3G-HLR functionalities. In this respect it is noted, that the terms “2G”and “3G” denote second and third generation mobile communicationfunctionalities, respectively.

With this configuration both the network and the UE 10 are able tomeasure the timing of signals and compute a location estimate of the UE10. Depending on the applied positioning method it is possible toutilize the corresponding configuration containing all needed entities.For instance, if network-based positioning is applied, the entities thatare involved in measuring the mobile's signal and calculating itslocation estimate are allocated to the network elements of the accessstratum. On the other hand, in case mobile-based or network-assistedmethods are used entities should be allocated to the UE 10.

The GMLC 50 contains functionality required to support LCS. In one PLMN,there may be more than one GMLC. The GMLC 50 is the first node theexternal LCS client 80 accesses in a GSM PLMN (i.e. the Le referencepoint is supported by the GMLC 50). The GMLC 50 may request routinginformation from the HLR/HSS 40 via a Lh interface. After performingregistration authorization, it sends positioning requests to either the2G-MSC 22, SGSNs 24, 32 or MSC server 34 and receives final locationestimates from the corresponding entity via the Lg interface. The UE 10may be involved in various positioning procedures. Specific UEinvolvement is specified in each of the positioning procedures mentionedin the 3 GPP specification TS 25305 for the UTRAN 30 and TS 43.059 forthe GERAN 20. The 2G-MSC 22 contains a functionality responsible for UEsubscription authorization and managing call related and non-callrelated positioning requests of LCS. The 2G-MSC 22 is accessible to theGMLC 50 via the Lg interface. The LCS functions of the 2G-MSC 22 arerelated to charging and billing LCS coordination, location requestauthorization and operation of the LCS services. If connected to the2G-SGSN 24 through a Gs interface, it checks whether the UE 10 is GPRSattached to decide whether to page the UE 10 on the A or Gs interface.

The MSC server 34 handles the same functionality as the 2G-MSC 22including charging and billing, LCS coordination, location requests,authorization and operation of the LCS services. The MSC server 34 isaccessible to the GMLC 50 via the Lg interface. Furthermore, the 2G- and3G-SGSNs 24, 32 contain a functionality responsible for UE subscriptionauthorization and managing positioning requests of LCS. The SGSNs 24, 32are accessible to the GMLC via the Lg interface. The LCS functions ofthe SGSNs 24, 32 are related to charging and billing, LCs coordination,location request, authorization and operation of the LCS services. TheSGSNs 24, 32 forward the CS paging request received from the Gsinterface to a base station subsystem or radio network controller of therespective access network.

The HLR/HSS 40 is accessible from the GMLC 50 via a Lh interface. For aroaming UE, the HLR/HSS 40 may be in a different PLMN.

Furthermore, a gsmSCF (GSM service control function) provides an Lcinterface to support access between the LCS and a network functionalityCAMEL (Customized Applications for Mobile Network Enhanced Logic)providing the mechanisms of Intelligent Network to a mobile user. Theprocedures and signaling associated with it are defined in the 3GPPspecification TS 23.078 and TS 29.002, respectively.

An important point is the possibility to address and indicate the targetUE 10 using a cellular identity, e.g. the MSISDN (Mobile StationIntegrated Services Data Network) or IMSI (International MobileSubscriber Identity), or the like. However, in the present case, theexternal LCS client 80 belongs to the IMS and thus uses an IMS identityin the location service request supplied to the GLMC 50. Therefore, amapping function is provided for mapping the IMS identity of the UE 10with a routing information required for accessing the HLR/HSS 40allocated to the target UE 10. Thereby, an IP addressing of the targetUE 10 can be performed without requiring an active PDP contextestablished between the target UE 10 and the external LCS client 80.

The Lh interface between the GMLC 50 and the HLR/HSS 40 may be based ona Mobile Application Part (MAP) protocol. This interface Lh is used bythe GMLC 50 to request a routing information to the serving MSC or SGSNof the particular target UE 10 whose location has been requested. The Lginterface is used by the GMLC 50 to convey the location request to therespective MSC or SGSN function currently serving the target UE 10.Furthermore, the Lg interface is used by the respective MSC or SGSNfunction to return location results to the GMLC 50.

For the LCS service, a MAP-SEND-ROUTING-INFO-FOR-LCS service is usedbetween the GMLC 50 and the HLR/HSS 40 to retrieve the routinginformation needed for routing a location service request to the servingMSC or SGSN function. In case the GMLC 50 receives a location servicerequest from the external LCS client 80, which contains an IMS identitythe GMLC 50 accesses the database 60 which may be arranged in the GMLC50 or as a separate external entity to derive the routing information tothe HLR/HSS 40. The IMS identity may be a public identity, such as a SIPURL, which is mapped by the HRL/HSS 40 to a cellular routinginformation, e.g. an MCC and MNC of the home network of the target ofthe UE 10. Using this cellular routing information the GMLC 50 accessesthe HLR/HSS 40 by a MAP query, e.g. a MAP-SEND-ROUTING-INFO-FOR-LCSmessage comprising the IMS identity, e.g. SIP URL. The HRL part of theHRL/HSS 40 may access the HSS part based on an interworking function toobtain the IMSI or any other cellular identity of the target UE 10 fromthe HSS part based on a corresponding mapping function. Using thiscellular identity, the GMLC 50 initiates a location service functionwithin the cellular network via the Lg interface. Thereby, an IMS LCSservice functionality can be provided in the UMTS/GSM networkarchitecture.

FIG. 2 shows a signaling diagram indicating basic signaling messages andprocedures required for the location service function. In particular,the external LCS client 80 requests the current location of the targetUE 10 from the GMLC 50 by using a LSC service request comprising the IMSID of the target UE 10 (step 1). In response thereto, GMLC 50 accessesthe database 60 and transfers the IMS ID to the database 60. Based onthe mapping function provided at the database 60 the correspondingcellular routing information MCC/MNC is returned to the GMLC 50. Then,the GMLC 50 uses this routing function to route a MAP query comprisingthe MS ID to the concerned HLR/HSS 40 identified by the MCC/MNC (step2). In response thereto, the HLR/HSS 40 returns the cellular identity(e.g. MSI) of the target UE 10 and a routing information (address of theserving network element) required for routing the LSC service request inthe cellular network (step 3). Now that the GMLC 50 knows both, the IMSIand location of the serving network element, the location serviceprocedure can be invoked in the cellular network (step 4). Finally, theGMLC 50 sends the location service response received from the cellularnetwork to the external LCS client 80 (step 5).

To implement the mapping function between the IMS identity and thecellular identity in the HLR/HSS 40, a new parameter has to beintroduced into the MAP query message, e.g. theMAP-SEND-ROUTING-INFO-FOR-LCS message. FIG. 3 indicates this newparameter, e.g. IMS identity as a conditional parameter for locationservice requests including an IMS identity. Thereby, the HLR/HSS 40 isin a position to provide the mapping function so as to retrieve thecellular identity of the target UE 10. Thus, theMAP-SEND-ROUTING-INFO-FOR-LCS service is enhanced so that it can carrywhatever public IMS identity is available to the GMLC 50. The GMLC 50 isarranged to put the IMS identity to the MAP-SEND-ROUTING-INFO-FOR-LCSservice request message instead of the conventionally used cellularidentity, e. g. IMSI or MSISDN. From the point of view of the HLR/HSS 40the new parameter is optional, i.e. if provided, a query to the HSS partis needed to map the public IMS identity to the cellular identity. TheHLR/HSS 40 then returns the retrieved cellular identity to the GMLC 50in a MAP-SEND-ROUTING-INFO-FOR-LCS service reply and the conventional CSor PS LCS methods can be used to locate the UE 10. The GMLC 50 may storethe mapping between the IMS identity and the cellular identity in itsinternal database or memory for further queries.

Furthermore, the preferred embodiment may be enhanced by returning allpublic IMS identities known in the HSS part of the HLR/HSS 40 to the GML50, so that any further location requests with other identities wouldnot require a HLR query at all as long as the location result in theGMLC 50 is still actual.

It is to be noted that the present invention is not restricted to theprovision of a location service in a IMS environment, but can be usedfor providing a location service in any overlay system having an ownoverlay identity allocated to the target mobile terminal. Thus, thepreferred embodiment may vary within the scope of the attached claims.

1. (canceled)
 2. A method comprising: receiving at a gateway node aservice request including an internet protocol multimedia subsystem(IMS) identity of a mobile terminal; determining to match the IMSidentity of the mobile terminal with one or more IMS identities of themobile terminal received from a subscriber database allocated to themobile terminal; and determining to locally retrieve routing informationand cellular identity of the mobile terminal associated with at leastone of the IMS identities of the mobile terminal that is matched withthe IMS identity.
 3. A method of claim 2, further comprising: causing,at least in part, a location service of a cellular network for themobile terminal based, at least in part, on the locally retrievedrouting information and cellular identity of the mobile terminal,without accessing the subscriber database.
 4. A method of claim 3,further comprising: receiving a previous service request including theat least one of matched IMS identity of the mobile terminal; accessing adatabase based on the at least one of matched IMS identity for a firstrouting information of the mobile terminal required for accessing thesubscriber database; accessing the subscriber database using the firstrouting information and deriving the routing information and cellularidentity of the mobile terminal associated with the at least one ofmatched IMS identity; and initiating a previous location service of thecellular network for the mobile terminal based on the derived routinginformation and cellular identity.
 5. A method of claim 4, furthercomprising: receiving the one or more IMS identities of the mobileterminal as available in the subscriber database based, at least inpart, on the access.
 6. A method of claim 2, wherein the internetprotocol multimedia subsystem identity is includes session initiationprotocol uniform resource locator.
 7. A method of claim 2, wherein thefirst routing information includes a country code and a network code ofthe mobile terminal.
 8. A method of claim 2, wherein the cellularidentity is a mobile subscriber integrated services digital networknumber or international mobile subscriber identity.
 9. An apparatuscomprising: at least one processor; and at least one memory includingcomputer program code for one or more programs, the at least one memoryand the computer program code configured to, with the at least oneprocessor, cause the apparatus to perform at least the following,receive at a gateway node a service request including an internetprotocol multimedia subsystem (IMS) identity of a mobile terminal;determine to match the IMS identity of the mobile terminal with one ormore IMS identities of the mobile terminal received from a subscriberdatabase allocated to the mobile terminal; and determine to locallyretrieve routing information and cellular identity of the mobileterminal associated with at least one of the IMS identities of themobile terminal that is matched with the IMS identity.
 10. An apparatusof claim 9, wherein the apparatus is further caused to: cause, at leastin part, a location service of a cellular network for the mobileterminal based, at least in part, on the locally retrieved routinginformation and cellular identity of the mobile terminal, withoutaccessing the subscriber database.
 11. An apparatus of claim 10, whereinthe apparatus is further caused to: receive a previous service requestincluding the at least one of matched IMS identity of the mobileterminal; access a database based on the at least one of matched IMSidentity for a first routing information of the mobile terminal requiredfor accessing the subscriber database; access the subscriber databaseusing the first routing information and deriving the routing informationand cellular identity of the mobile terminal associated with the atleast one of matched IMS identity; and initiate a previous locationservice of the cellular network for the mobile terminal based on thederived routing information and cellular identity.
 12. An apparatus ofclaim 11, wherein the apparatus is further caused to: receive the one ormore IMS identities of the mobile terminal as available in thesubscriber database based, at least in part, on the access.
 13. Anapparatus of claim 9, wherein the internet protocol multimedia subsystemidentity is includes session initiation protocol uniform resourcelocator.
 14. An apparatus of claim 9, wherein the first routinginformation includes a country code and a network code of the mobileterminal.
 15. An apparatus of claim 9, wherein the cellular identity isa mobile subscriber integrated services digital network number orinternational mobile subscriber identity.
 16. A computer-readablestorage medium carrying one or more sequences of one or moreinstructions which, when executed by one or more processors, cause anapparatus to at least perform the following steps: receiving at agateway node a service request including an internet protocol multimediasubsystem (IMS) identity of a mobile terminal; determining to match theIMS identity of the mobile terminal with one or more IMS identities ofthe mobile terminal received from a subscriber database allocated to themobile terminal; and determining to locally retrieve routing informationand cellular identity of the mobile terminal associated with at leastone of the IMS identities of the mobile terminal that is matched withthe IMS identity.
 17. A computer-readable storage medium of claim 16,wherein the apparatus is caused to further perform: causing, at least inpart, a location service of a cellular network for the mobile terminalbased, at least in part, on the locally retrieved routing informationand cellular identity of the mobile terminal, without accessing thesubscriber database.
 18. A computer-readable storage medium of claim 17,wherein the apparatus is caused to further perform: receiving a previousservice request including the at least one of matched IMS identity ofthe mobile terminal; accessing a database based on the at least one ofmatched IMS identity for a first routing information of the mobileterminal required for accessing the subscriber database; accessing thesubscriber database using the first routing information and deriving therouting information and cellular identity of the mobile terminalassociated with the at least one of matched IMS identity; and initiatinga previous location service of the cellular network for the mobileterminal based on the derived routing information and cellular identity.19. A computer-readable storage medium of claim 18, wherein theapparatus is caused to further perform: receiving the one or more IMSidentities of the mobile terminal as available in the subscriberdatabase based, at least in part, on the access.
 20. A computer-readablestorage medium of claim 16, wherein the internet protocol multimediasubsystem identity is includes session initiation protocol uniformresource locator.
 21. A computer-readable storage medium of claim 16,wherein the first routing information includes a country code and anetwork code of the mobile terminal.